During the advancement or manipulation of a pipe string in a wellbore such as a drillstring or a coil tubing string, it is often prudent to jar, vibrate, or oscillate the pipe string as an aid in overcoming frictional forces between the pipe string and the interior surface of the wellbore. Vibrations convert static frictional forces to kinetic frictional forces. For this application, a device or apparatus incorporated with a wellbore pipe string to induce pipe string vibration is called a Friction Reducing Apparatus and will be referred to as a “FRA”.
A FRA may utilize reciprocating impact elements that move back and forth along the axis of the pipe string and which rely upon the mass and velocity of the reciprocating impacting element to produce pipe string vibration. A FRA may also employ eccentrically weighted rotating masses, eccentric shafts or rods, or rotatable impact elements that rotate about the longitudinal axis of the drill or pipe string to strike an impact anvil to apply a rotational or torsional vibration to the pipe string. A FRA with these types of impact elements typically only generates vibration at a localized segment of the pipe string.
A FRA may also utilize Moineau power sections such as those used in downhole mud motors or pumps to induce pipe string vibration. Moineau power sections usually have sealing mechanisms comprising rubber or rubber-like elastomers. The rubber or rubber-like elastomers of these sealing mechanisms are subject to deterioration over time due to the effects of wellbore temperatures and pressures, drilling fluids, wellbore chemicals, and contaminants or debris in the wellbore.
Many drilling and work-over operations utilize downhole tools or devices incorporated on the pipe string and run into the wellbore. Often an object, generally a ball or dart, pumped through the pipe string from the well surface, activates these downhole tools and devices. The balls or darts are used to close off ports or shift sleeves or pistons. The typical FRA has no direct circulation path or other means to allow a ball or dart to circulate past the FRA to a tool positioned on the pipe string further downhole. Consequently, a ball or dart cannot be circulated through the typical FRA further down the pipe string. If such a downhole tool or device is needed, it cannot be run and activated downhole with the typical FRA. When a typical FRA is utilized on the pipe string, the FRA must be removed before a ball or dart activated tool is used on the pipe string requiring at least one additional trip into and out of the wellbore which is time consuming and costly.
Because of the disadvantages associated with a typical FRA, there is a need for a pipe string FRA that will induce vibration to a larger percentage of the pipe string, or the entire pipe string, without being susceptible to the negative effects of temperature and pressure and other factors associated with a wellbore environment. There is also a need for a pipe string FRA and that will allow the use of the FRA in conjunction with a ball or dart activated downhole tools and devices.